Techniques for Controlling Charging of Batteries in an External Charger and an Implantable Medical Device

ABSTRACT

Disclosed are charging algorithms implementable in an external charger for controlling the charging of both an external battery in the external charger and an implant battery in an implantable medical device. Because full-powered simultaneous charging of both batteries can generate excessive heat in the external charger, the various charging algorithms are designed to ensure that both batteries are ultimately charged, but in a manner considerate of heat generation. In some embodiments, the charging algorithms prevent simultaneous charging of both batteries by arbitrating which battery is given charging precedence at a given point in time. In other embodiments, the charging algorithms allow for simultaneous charging of both batteries, but with at least one of the batteries being only weakly charged at low power levels. In other embodiments, the temperature generated in the external charger is monitored and used to control the charging algorithm. In these embodiments, if a safe temperature is exceeded, then the charging algorithms change to new temperature-reducing schemes which still allow for both batteries to be ultimately charged.

FIELD OF THE INVENTION

The present invention relates generally to implantable medical devicesystems, and in particular to systems employing an external chargerapparatus.

BACKGROUND

Implantable stimulation devices generate and deliver electrical stimulito nerves and tissues for the therapy of various biological disorders,such as pacemakers to treat cardiac arrhythmia, defibrillators to treatcardiac fibrillation, cochlear stimulators to treat deafness, retinalstimulators to treat blindness, muscle stimulators to producecoordinated limb movement, spinal cord stimulators to treat chronicpain, cortical and deep brain stimulators to treat motor andpsychological disorders, occipital nerve stimulators to treat migraineheadaches, and other neural stimulators to treat urinary incontinence,sleep apnea, shoulder sublaxation, etc. Implantable stimulation devicesmay comprise a microstimulator device of the type disclosed in U.S.Patent Application Publication 2008/0097529, or larger types ofstimulators such as spinal cord stimulators or pacemakers for example.

Microstimulator devices typically comprise a small,generally-cylindrical housing which carries electrodes for producing adesired electric stimulation current. Devices of this type are implantedproximate to the target tissue to allow the stimulation current tostimulate the target tissue to provide therapy. A microstimulator's caseis usually on the order of a few millimeters in diameter by severalmillimeters to a few centimeters in length, and usually includes orcarries stimulating electrodes intended to contact the patient's tissue.However, a microstimulator may also or instead have electrodes coupledto the body of the device via a lead or leads. A multi-electrodemicrostimulator 10 having a single anode (Ea) and several selectablecathodes (Ec1 et seq.) in shown in FIG. 1. Further details regardingsuch a microstimulator 10 can be found in the above-referenced '529application.

Implantable microstimulators 10 are typically powered by an internalbattery, which periodically needs to be recharged. Such recharging isusually accomplished by an external charger, which produces a magneticfield to ultimately induce a current in a coil in the implant. Thisinduced current is rectified, and used to charge the implant battery.

Recharging the implant battery by magnetic induction works well, andallows the implant battery to be charged wirelessly and transcutaneously(i.e., through the patient's tissue). However, such techniques alsosuffer from heat generation. In particular, the external charger canheat up, and if it gets too hot may burn the patient.

The inventors have noted that this problem of external chargeroverheating can be exacerbated if the external charger itself requiresrecharging. In this regard, note that the external charger may toocontain a rechargeable battery, whose power is used to produce themagnetic field to charge the implant's battery. If the externalcharger's battery needs recharging, this provides an additional heatload on the external charger, particularly if the external charger'sbattery and the implant's battery require recharging at the same time.The inventors believe that a solution to this problem of excessiveheating in an external charger is therefore indicated, and thisdisclosure provides solutions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a microstimulator device of the prior art.

FIG. 2 illustrates the microstimulator of FIG. 1 as implanted, and showsexternal charging components used for charging a battery in themicrostimulator.

FIGS. 3A and 3B illustrate circuitry useable in the external chargingcomponents to implement the disclosed charging algorithms that regulatecharging of both an external battery in the external charging componentsand an implant battery in the microstimulator.

FIGS. 4 and 5 illustrate charging algorithms that charge one of theexternal or implant batteries first, and then the other.

FIGS. 6A and 6B illustrate a charging algorithm that alternates betweencharging the external battery and the implant battery.

FIGS. 7A-8B illustrates charging algorithms that allow for simultaneouscharging of the external and implant batteries, but only allows one ofthose batteries to be weakly charged at low power.

FIG. 9 illustrates a charging algorithm that allows for simultaneouscharging of the external and implant batteries, but with both being onlyweakly charged at low power.

FIGS. 10 and 11 illustrates charging algorithms that change to reduceheat generation depending on the temperature sensed in the externalcharging components.

DETAILED DESCRIPTION

Disclosed are charging algorithms implementable in an external chargerfor controlling the charging of both an external battery in the externalcharger and an implant battery in an implantable medical device. Becausefull-powered simultaneous charging of both batteries can generateexcessive heat in the external charger, the various charging algorithmsare designed to ensure that both batteries are ultimately charged, butin a manner considerate of heat generation. In some embodiments, thecharging algorithms prevent simultaneous charging of both batteries byarbitrating which battery is given charging precedence at a given pointin time. In other embodiments, the charging algorithms allow forsimultaneous charging of both batteries, but with at least one of thebatteries being only weakly charged at low power levels. In otherembodiments, the temperature generated in the external charger ismonitored and used to control the charging algorithm. In theseembodiments, if a safe temperature is exceeded, then the chargingalgorithms change to new temperature-reducing schemes which still allowfor both batteries to be ultimately charged.

FIG. 2 shows a microstimulator 10 as implanted in a patient. In theillustrated application, the microstimulator 10 is implanted within thehead of a patient, although this is merely exemplary and could beimplanted elsewhere. When implanted in the head, the microstimulator 10can be used to stimulate the occipital nerves, which can be beneficialin the treatment of migraine headaches for example. More than onemicrostimulator 10 may be implanted, but only one is shown forconvenience.

Also shown in FIG. 2 are various external charging components 20, thecircuitry details of which are shown in FIGS. 3A and 3B. The basicfunction of the external charging components 20 is to wirelesslyrecharge an implant battery 86 in the microstimulator 10. The implantbattery 86 provides the power for the microstimulator 10, including thecircuits that ultimately provide therapeutic pulses to themicrostimulator's electrodes. The external charging components 20 can beused to recharge the implant battery 86 as needed, perhaps on a dailybasis. Together, the external charging components 20 can be referred toas the external charger.

The external charging components 20 comprise a head piece 22 and a coilcontroller 24. As shown in FIG. 3A, the head piece 22 comprises a coil70 covered or encapsulated in a cover 71. The cover 71 is shaped to becomfortably held in place on the back of the head near the site at whichthe microstimulator(s) 10 is implanted, and may include a head band forexample. When energized, coil 70 produces a magnetic charging field,which is received transcutaneously (i.e., through the patient's tissues)at a charging coil 80 within the microstimulator 10. The current inducedin the charging coil 80 is rectified (82) to a suitable DC level (Vdc2)and charges the implant battery 86, perhaps using a battery chargingcircuit 84 as an intermediary. The implant battery will be deemedsufficiently charged when its voltage exceeds some pre-determined level,e.g., voltage threshold Vt2 as will be discussed in further detailbelow.

As its name implies, the coil controller 24 controls the charging coil70 in the head piece 22, and contains a wireless transmitter 68, whichis used to drive the coil 70 to produce the necessary magnetic chargingfield. The transmitter 68 creates an alternating current across the coil70, and can comprise a resonant circuit such as an inductor-capacitor(L-C) tank circuit, as shown in FIG. 3B. The drive signal to the tankcircuit sets the frequency of the produced wireless magnetic chargingfield, which might be in the neighborhood of 80 kHz for example.Transistor switches allow the tank circuit's power supply, V+, to beplaced across the L-C series circuit with alternating polarities.Further details concerning this type of tank circuit can be found inU.S. patent application Ser. No. 12/368,385, filed Feb. 10, 2009. Thetransmitter 68 is controlled by a microcontroller 60 within the coilcontroller 24. The coil controller 24 contains other electronics whichwill be discussed in further detail later. Such coil controller 24electronics can be placed inside a plastic housing 27 for example, whichhousing may carry a user interface (e.g., an on/off button, inputbuttons, LEDs, a display, speakers, etc.) if desired.

External charging components 20 also include a plug 26 for tapping intoan AC power source such as a wall outlet or other source. The plug 26includes transformer and rectifier circuitry not shown, and so providespower to the coil controller 24 in the form of a DC voltage, Vdc1.However, such transformer and rectifier circuitry can also exist in thehousing 27 of the coil controller itself, although this is not shown forconvenience. Plug 26 can be coupled to the coil controller at connector25.

Coil controller 24 includes a rechargeable external battery 64, whichcan be recharged using the DC voltage, Vdc1, provided by the plug 26. Toregulate the charging current (Ibat1) and otherwise protect the externalbattery 64, battery charging circuitry 62 is used. Such batterycircuitry 62 is commercially available in the art, and may compriseproduct LT4002 from Linear Technology for example. Battery circuitry 62is controlled by microcontroller 60. Like the implant battery 86, theexternal battery 64 in the coil controller 24 will be deemedsufficiently charged when its voltage exceeds some threshold, e.g., Vt1as discussed further below.

After the external battery 64 is recharged, the plug 26 can bedisconnected from connector 25 on the coil controller 24. This allowsthe coil controller 24 to be used without being tethered to a wallsocket for example, which allows a patient wishing to recharge theinternal battery 86 in her microstimulator 10 “on the go”. Whendisconnected from the plug 26, the coil controller 24 receives itoperating power exclusively from the external battery 64, Vbat1, whichwould be used to power the controller's electronics and (mostsignificantly from a power consumption standpoint) the transmitter 68used to energize coil 70. Powering of the transmitter 68, i.e.,provision of the power supply voltage V+ to be applied to thetransmitter's tank circuit, occurs via a switch 66 operating undercontrol of the microcontroller 60.

Although the coil controller 24 can be decoupled from the plug 26, theywould be connected when charging the external battery 64, or whencharging the external battery 64 and the implant battery 86 at the sametime. When plug 26 is coupled to the coil controller 24, either thevoltage from the plug (Vdc1), or the voltage of the external battery 64(Vbat1) depending on its level of depletion, can be used to providepower to the transmitter 68. Switch 66 controls whether Vdc1 or Vbat1 ischosen as the power source V+ for the transmitter 68. (Optionalregulator 98 is ignored for now, but will be discussed later).

Before discussing the various manners in which the external chargingcomponents 20 can be used in accordance with embodiments of theinvention, various portions of the external charging components 20 couldbe integrated. For example, while it is convenient to separate the coil70 in the head piece 22 from the coil controller 24 for the occipitalnerve stimulation application illustrated in FIG. 2, such separation isnot necessary. In a spinal cord stimulator application for instance, thecoil 70 could be integrated within housing 27 of the coil controller 24,such as is shown in U.S. Patent Publication 2008/0027500 for example.

As noted in the Background, operation of the external chargingcomponents 20 to recharge the implant battery 86 can cause heating. Inparticular, the inventors have noticed that the transmitter circuit 68in the coil controller 24 is subject to heating during creation of themagnetic charging field. The inventors have also noticed that additionalheat can be generated in the coil controller 24 if the external battery64 too requires charging, i.e., if the coil controller is coupled to theplug 26 and the battery charging circuitry 62 is activated to charge theexternal battery 64. The battery charging circuitry 62 provides asignificant source of additional heating. When heat from the batterycharging circuitry 62 is combined with heat from the transmittercircuitry 68, the coil controller 24 can get excessively hot. Becausethe coil controller 24 can be held against a patient's skin using arestraining belt for example, the risk of injury during simultaneouscharging of the external battery 64 and the implant battery 86 isproblematic.

FIGS. 4-11 disclose various charging algorithms in which implant batterycharging and external battery charging are controlled to preventoverheating the coil controller 24. Each disclosed algorithm can bedesigned to automatically run, for example: when the patient selects tocharge the implant battery 86 via a selection made on the coilcontroller 24's user interface (not shown); when the coil controller 24is turned on; when the coil controller 24 is plugged into an AC powersource using plug 26; or upon the occurrence of any other condition inwhich it is logical or necessary to charge either or both of the implantbattery 86 or the external battery 64 in the coil controller 24. Oneskilled in the art will understand that the disclosed algorithms can beimplemented by the microcontroller 60 in the coil controller 24.

A group of steps 100 define example initial conditions which set thestage for implementation of the invention, which steps 100 areessentially geared to determining whether charging of both the implantbattery 86 in the microstimulator 10 and the external battery 64 in thecoil controller 24 is warranted and possible. Because these initialsteps can be the same for each of the disclosed embodiments of FIGS.4-11, they are repeated at the beginning of those figures. However,these initial steps 100 are merely illustrative, and could be deleted,altered, or added to in useful implementations.

As a first initial step, the microcontroller 60 in the coil controller24 determines if it is coupled via plug 26 to an external power sourcesuch as a wall socket, which determination can be made by assessingwhether the Vdc1 is present. If not, the external battery 64 cannot becharged, and if necessary, the implant battery 86 can be charged.Because Vdc1 is not present, switch 66 would route the external batteryvoltage, Vbat1, to the transmitter 68's power supply V+. If the externalbattery 64 is sufficient to produce a magnetic charging field, thencharging of the implant battery 86 can commence as normal; if notsufficient, then charging would terminate in typical fashion.

If the coil controller 24 is plugged in and Vdc1 is present, nextinitial steps 100 ask whether either or both of the external battery 64or the implant battery 86 require charging. This can comprise assessingwhether the voltage of those batteries 64 and 86, i.e., Vbat1 and Vbat2respectively, is below some capacity threshold voltage, i.e., Vt1 andVt2 respectively. Of course, other methods exist for determining batterycapacity, and comparison to a threshold voltage should be understood asmerely exemplary.

Determining the voltage of external battery 64, Vbat1, is straightforward for the microcontroller 60 in the coil controller 24, becausethe external battery is within the controller; any well knownanalog-to-digital or comparator circuitry can be used determine Vbat1and/or its relation to threshold Vt1. Determination of the voltage ofthe implant battery 86, Vbat2, requires similar measuring circuitry atthe microstimulator 10, and telemetry of the determined Vbat2 value tothe coil controller 24. Such telemetry can occur using load shiftkeying, in which the impedance of charging coil 80 in themicrostimulator 10 is modulated with the battery voltage data, causingdetectable reflections in the active transmitter coil 70. Such a meansof back telemetry from the microstimulator 10 to the external chargingcoil 70 is well known and is discussed further in U.S. patentapplication Ser. No. 12/354,406, filed Jan. 15, 2009.

If the implant battery 86 does not require charging (i.e., Vbat2>Vt2)but the external battery 64 requires charging (Vbat1<Vt1), then theexternal battery is charged using Vdc1. Specifically, the batterycharging circuitry 62 is enabled and the transmitter 68 is disabled bythe microcontroller 60. Because the transmitter 68 is disabled, theposition of switch 66 does not matter.

By contrast, if the implant battery 86 requires charging (i.e.,Vbat2<Vt2) but the external battery 64 does not require charging(Vbat1>Vt1), then the implant battery is charged using Vbat1.Specifically, the battery charging circuitry 62 is disabled, and thetransmitter 68 is enabled. In this condition, both Vbat1 and Vdc1 arepresent, and either could be passed by the switch 66 to power thetransmitter 68 (V+). However, it can be preferable for switch 66 toapply the external battery voltage, Vbat1, to the transmitter. This isbecause the transmitter 68 and coil 70 are normally optimized to work ina non-tethered environment in which the coil controller 24 is portableand not plugged in, such that power to energize the coil 70 can comeonly from the external battery 64. However, this is not strictlyrequired, and any power supply (including Vdc1) can be used to power thetransmitter 68 to produce the magnetic charging field for the implantbattery 86.

If it is determined that both the implant battery 86 and the externalbattery 64 require charging (i.e., Vbat2<Vt2 and Vbat1<Vt1), then thealgorithm exits initial steps 100 and begins steps designed toeventually charge both batteries in a manner considerate of heatgeneration in the coil controller 24.

In steps 110 of FIG. 4, although both the external battery 64 and theimplant battery 86 require charging, charging of the implant battery 62is given precedence, and charging of the external battery 64 does notcommence until the implant battery 62 is fully charged. Therefore, thetransmitter 68 is enabled by the microcontroller 60 in the coilcontroller 24 to produce a magnetic charging field for charging theimplant battery 86. Because the external battery voltage Vbat1 isinsufficient (<Vt1), the power provided to the transmitter 68 fromswitch 66 comprises the rectified voltage, Vdc1, from plug 26. Asmentioned earlier, this may not be optimally efficient for thetransmitter 68 and coil 70, which are generally tuned to operate at afully charged external battery voltage (i.e., Vbat1=Vt1). Still,charging with Vdc1 (or some regulated version thereof, not shown), willstill be sufficient under the circumstance, even if not optimal. Becauseprecedence is initially given to charging of the implant battery 86, thebattery charging circuit 62 for external battery 64 is automaticallydisabled by the microcontroller 60.

After some time, and preferably on a periodic basis, the implant batteryvoltage, Vbat2, is telemetered to the coil controller 24 in the mannerdiscussed previously, and is assessed relatively to its threshold, Vt2.If Vbat2 is still less than its threshold Vt2, then charging of theimplant battery 86 continues in the manner just discussed. However, whenthe implant battery 86 becomes sufficiently charged (Vbat2>Vt2), thencharging of the implant battery 86 can cease, and charging of theexternal battery 64 can begin. Microcontroller 60 affects this byautomatically enabling the battery charging circuit 62 in the coilcontroller and disabling the transmitter 68. This allows Vdc1 to be usedto charge the external battery 64.

By the practice of steps 110, notice that the battery charging circuitry62 and the transmitter 68 are not simultaneously enabled, even thoughthe conditions of their respective batteries 64 and 86 might otherwisesuggest that such simultaneity is warranted. Controlling two of the mainheat sources in the coil controller 24 in this fashion reduces thelikelihood that the coil controller 24 will overheat. As noted earlier,this improves patient safety.

Steps 120 in FIG. 5 are similar to steps 110 in FIG. 4, except thatprecedence is given to charging the external battery 64. Thus, eventhough both batteries 64 and 86 require charging, steps 120 start byenabling the battery charging circuitry 62 to charge external battery 64using Vdc1. The transmitter 68 is disabled to prevent generation of amagnetic charging field and charging of the implant battery 86. Thevoltage of the external battery, Vbat1, is checked on a periodic basis.If that voltage is less than its threshold (i.e., Vbat1<Vt1), thencharging of the external battery 64 continues. Eventually, when theexternal battery voltage exceeds its threshold (i.e., Vbat1>Vt1), thenthe implant battery 86 is charged, and the external battery 64 isprevented from further charging: specifically, the transmitter 68 isenabled, and the battery charging circuitry 62 is disabled. Because theexternal battery 64 is sufficiently charged before charging of theimplant battery 86, switch 66 preferably passes the external batteryvoltage, Vbat1, to the enabled transmitter 68. Again, this is preferredas an optimal match to the transmitter 68 and coil 70, but is notstrictly necessary, as the enabled transmitter 68 may also be power byVdc1, a regulated version thereof, or any other power source.Regardless, steps 120 again prevent simultaneous enablement of twoprimary heat sources in the coil controller 24—battery charging circuit62 and transmitter 68—thus reducing heat and improving patient safety.

Steps 130 in FIG. 6A similarly prevent the simultaneous activation ofthese two heat sources, but do so by enabling them in an alternatingfashion, such that one of the batteries 64 and 86 is charged for a timeperiod, then the other for a time period, then the first again, then theother again, etc.

As illustrated, upon leaving initial steps 100, the implant battery 86is charged first by disabling the battery charging circuitry 62 andenabling transmitter 68. Again, because the external battery 64 at thispoint is insufficiently charged, switch 66 provides Vdc1 instead topower the transmitter 68. Such charging of the implant battery 86 occursfor a time period t2, which may be set by the designers of the externalcharging components 20, and which may comprise 60 seconds for example.Once time t2 is exceeded, and assuming that the implant battery 86 isstill undercharged (Vbat2<Vt2), then the external battery 64 is charged.This occurs by enabling the battery charging circuitry 62 and disablingthe transmitter 68, which allows Vdc1 to charge the external battery 64.Charging of the external battery 64 continues in this fashion until theexpiration of another time period t1. (t1 may equal t2). If after t1,the external battery 64 remains insufficiently charged (Vbat1<Vt1), thenthe implant battery 86 is once again charge for its time t2, etc. Suchinterleaving of the charging of the two batteries 64 and 86 is shown inFIG. 6B.

This back-and-forth process continues until either the external battery64 or the implant battery 86 achieves a suitable charge, i.e., untileither Vbat1>Vt1 or Vbat2>Vt2. When either of these conditions occurs,the suitably charged battery is disconnected, and the not-yet-fullycharged battery is given precedence by the coil controller 24, as shownby the steps at the bottom of FIG. 6A. For example, if it is determinedthat the implant battery 86 is fully charged (Vbat2>Vt2), then batterycharging circuit 62 is enabled, and transmitter 68 is disabled, as shownat the bottom left of FIG. 6A. This curtails charging of the implantbattery 86, and allows the external battery 64 to be charged withoutinterruption until complete (i.e., until Vbat1>Vt1). By contrast, if itis determined that the external battery 64 is fully charged (Vbat1>Vt1),then battery charging circuit 62 is disabled, and transmitter 68 isenabled, as shown at the bottom right of FIG. 6A. This curtails chargingof the external battery 64, and allows the implant battery 86 to becharged without interruption until complete (i.e., until Vbat2>Vt2).

The embodiments disclosed in steps 140 in FIG. 7A and steps 150 in FIG.8A also reduce heat generation in the coil controller 24 in the eventthat both the external battery 64 and the implant battery 86 requirerecharging. However, unlike previous embodiments, steps 140 and 150permit simultaneous charging of both batteries 64 and 86. However, oneof the batteries in steps 140 and 150 is not charged to a full extent.Instead, such one battery is only “weakly” charged, i.e., charged with apower less than would be indicated were that one battery to be chargedby itself. As a result, the average power level drawn by the combinationof the battery charger circuit 62 and the transmitter 68 is reduced whencompared to the average power level used when both batteries are fullycharged together.

In the embodiment illustrated in FIG. 7A, after performance of theinitial steps 100 which determine that both batteries 64 and 86 requirecharging, a first step 145 provides full charging power to the implantbattery 86, but at the same time also allows for weak charging of theexternal battery 64. Full charging of the implant battery 86, as inearlier embodiments, entails enabling the transmitter 68, and settingthe switch 66 to Vdc1.

Simultaneous weak charging of the external battery 64 in step 145 can beaccomplished in different ways, a couple of which are illustrated inFIG. 7B. Each of the illustrated ways involve controlling the externalbattery charging current, Ibat, to an average that is less than itsmaximum, Ibat(max), where Ibat(max) denotes the current that is normallyused to fully charging the external battery 64. In the first wayillustrated at the top of FIG. 7B, weak charging involves merelylowering the external battery charging current from its maximum value,e.g., to perhaps one-half of Ibat(max). In the second way illustrated atthe bottom, the external battery charging current is made to duty cyclebetween Ibat(max) and 0; in this simple example, the average Ibatcurrent would again be approximately one-half Ibat(max). In either case,the average power level used to charge the external battery is reducedcompared to the power levels used when that battery is charged byitself. Control of the external battery charging current Ibat isperformed by the battery charging circuit 62 under control of themicrocontroller 60. Such control can come in the form of optimal controlsignal(s) 95 (FIG. 3) between the microcontroller 60 and the batterycharging circuit 62, which signal(s) 95 can specify full charging orsome relative amount of weak charging, etc.

During simultaneous charging of the external battery 64 and the implantbattery 86, the capacities of these batteries are periodically checked.If neither is fully charged, the just-described simultaneous charging ofstep 145 continues. If the implant battery become fully charged first,i.e., if Vbat2>Vt2, as might be expected because it is givenfull-charging precedence by step 145, then charging of the implantbattery 86 ceases: transmitter 68 is disabled. At this point, chargingof the external battery 64 can occur as normal, i.e., with a fullcharging current Ibat(max) as indicated by signal 195 (FIG. 3). If theexternal battery 64 becomes fully charged first, i.e., if Vbat1>Vt1,then charging of the external battery 64 ceases, and charging of theinternal battery 86 continues: battery charging circuit 62 is disabled,and transmitter 68 continues to be enabled. Because the external battery64 is now charged, switch 66 can pass that battery's voltage, Vbat1, tothe transmitter 68, which as indicated earlier, is preferable from atuning standpoint.

Steps 150 in FIG. 8A are similar to steps 140 in FIG. 7A, except that instep 155 of this embodiment, full charging power is provided to theexternal battery 64, while the implant battery 86 is simultaneouslyweakly charged. Full charging of the external battery 64 occurs asbefore, by enabling battery charging circuit 62 to provide full chargingpower Ibat(max) to the external battery 64.

By contrast, less than full power levels, at least on average, isprovided to the transmitter 68 to provide a less-than-full-powermagnetic charging field, which in turn charges the implant battery 86 toa lesser extent. A couple of ways for achieving a lower power draw inthe transmitter 68 are shown in FIG. 8B. In the first way illustrated atthe top of FIG. 8B, the transmitter is selectively enabled and disabled(i.e., duty cycled), such that it produces a full strength magneticcharging field at some times, but at other times is off. In the secondway illustrated in FIG. 8B, the power supply for the tank circuit in thetransmitter 68, V+ (see FIG. 3B), is lowered from Vdc1 (the voltagenormally used by the transmitter if the external battery 64 is notsufficiently charged) to Vdc1(ref), which comprises a stepped-downvoltage produced by optional regulator 98 as shown in FIG. 3A. In eithercase, on average, the average power level of the transmitter 68 islessened compared to when the implant battery is charged by itself, asis the magnitude of the resulting magnetic charging field.

During simultaneous charging of the external battery 64 and the implantbattery 86 in step 155, the capacities of these batteries areperiodically checked. If neither is fully charged, the simultaneouscharging continues. If one of the batteries is charged first, thenfurther charging of that batteries ceases and charging of the otherbattery occurs as normal. As these latter steps in 150 are the same aswas described with respect to steps 140 in FIG. 7A, they are not againrepeated.

Regardless of whether the embodiment of FIG. 7A or 8A is considered,simultaneous charging occurs, but with reduced power draw by either thebattery charging circuit 62 or the transmitter 68. As both of thesecomponents have been noticed as significant in generating heat in thecoil controller 24, mitigating the power draw in at least one of thesecomponents helps to address the heat problem created by the need tocharge both the external battery 64 and the implant battery 86, thusproviding a safer solution.

FIG. 9 comprises an approach similar to those of FIGS. 7A and 8A in thatit allows simultaneous charging of both the external battery 64 and theimplant battery 86, but such charging occurs by weakly charging both ofthese batteries simultaneously. Therefore, as shown in step 165, shouldboth batteries need charging, the external battery 64 is charged with areduced power draw in the battery charging circuit 62 (e.g., with alower average Ibat as shown in FIG. 7B) and the internal battery 86 ischarged using a lower power draw at the transmitter 68 (e.g., as shownin FIG. 8B). Once either battery 64 or 86 is fully charged, then theother can be charged at full power levels, as discussed earlier. Thus,the embodiment of FIG. 9 would cut power draw in both the batterycharging circuitry 62 and the transmitter 68 simultaneously, evenfurther lowering the risk (when compared to FIGS. 7A and 8A) thatsimultaneous activation of these circuits would cause overheating of thecoil controller 24.

FIG. 10 provides yet other embodiments for a charging algorithm forcharging both the external battery 64 in the coil controller 24 and theimplant battery 86 in the microstimulator 10. As already mentioned, theinventors have noted that simultaneous activation of the batterycharging circuit 62 and the transmitter 68 raises concerns about heatgeneration in the coil control 24. Accordingly, the embodiment of FIG.10 factors consideration of the actual temperature of the coilcontroller 24 into consideration when controlling the charging of bothbatteries. Thus, and referring to FIG. 3A, optional temperaturesensor(s) 69 is provided in the coil controller 24, which provideinformation concerning the temperature, T, to the microcontroller 60. Ifa plurality of temperature sensors 69 are used, the indicatedtemperature T can comprise an average of temperature sensed by eachsensor 69 for example. Temperature sensor(s) 69 can comprisethermocouples, thermistors, or the like, and can be affixed at anylocation in or on the housing 27 of the coil controller 24.

After initial steps 100 during which it is concluded that both externalbattery 64 and implant battery 86 require charging, step 175 allows bothof these batteries to be fully charged at maximum power levels. Thisentails enabling the battery charging circuit 62, enabling thetransmitter 68, and setting switch 66 to Vdc1. By this configuration,Vdc1, the power provided by the plug 26, simultaneously fully chargesthe external battery 64 and powers the transmitter 68 for full poweringof the implant battery 86.

As full power level charging of both batteries 64 and 86 progresses asprovided in step 175, three conditions are continually monitored,logically on a periodic basis: the capacity of batteries 64 and 86 insteps 176, and the temperature of the coil controller 24 in step 177.Monitoring the capacities of the batteries in steps 176 is similar tosteps 147 and 157 in FIGS. 7A and 8A respectively, and thus are notfurther discussed. However, step 177 provides a significant differencefrom earlier embodiments, because it ascertains whether the temperatureof the coil controller 24 is higher than a predetermined temperature,Tmax. Tmax may represent a maximum safe temperature as determined by thedesigner of the external charging components 20. For example, Tmax maycomprise 41° C., as temperatures above this limit may have the abilityto hurt a patient after prolong contact.

Should the temperature exceed this safe value Tmax in step 177, then,and as shown in step 179, charging of the batteries 64 and 86 can bemodified so that both batteries 64 and 86 are not simultaneouslycharged, or not simultaneously charged to a full extent. This cancomprise employing any of the heat-reducing charging techniquespreviously disclosed in FIGS. 4-9 for example. Thus, in step 179: theimplant battery can be charged, followed by charging of the externalbattery (Steps 110; FIG. 4), and/or: the external battery can becharged, followed by charging of the implant battery (Steps 120; FIG.5), and/or; the external battery and implant battery can be charged inalternative fashion (Steps 130; FIG. 6A), and/or; the power used tocharge external battery can be reduced (Steps 140; FIG. 7A), and/or; thepower used to charge implant battery can be reduced (Steps 150, FIG. 8),and/or; the power used to charge implant battery and external batterycan be reduced (Steps 160, FIG. 9), etc.

Implementation of the heat-reducing charging techniques in step 179would be expected to lower the temperature of the coil controller 24when compared to full-blown simultaneous charging of the external 64 andimplant 86 batteries (step 175). Accordingly, as an optional step in theprocess depicted in FIG. 10, should the temperature of the coilcontroller 24 once again fall below Tmax (Temp<Tmax; see step 177), thensimultaneous full charging of both batteries 64 and 86 can once againcommence. If not, then at least one temperature mitigation technique ofstep 179 continues to operate. However, this is optional, and instead,once Tmax is exceeded, the charging system can be constrained by thetemperature mitigating techniques of step 179, without return to fullblown charging of both batteries as in step 175.

To summarize, the charging algorithm of FIG. 10 allows both batteries 64and 86 to be charged at full power (step 175), until the temperature ofthe coil controller 24 exceeds a maximum safe temperature, Tmax (step177). Once this temperature is exceeded, the microcontroller 60 employsa temperature-reducing scheme (step 179) designed to not simultaneouslycharge both batteries 64 and 86, at least to a full extent. Once thetemperature of the coil controller 24 cools (Temp<Tmax) (step 177) thenfull charging of both batteries 64 and 86 can once again continue ifdesired.

FIG. 11, like FIG. 10, also controls the charging algorithm inaccordance with the temperature of the coil controller 24. However, inconstant to step 157 in FIG. 10 which allows for simultaneous fullcharging of the both the external battery 64 and the implant battery 86,step 185 in FIG. 11 only allows a temperature-reducing scheme to beused. This step 185 can comprise use of any of the techniques discussedearlier in FIGS. 4-9 or combinations thereof. After implementation of aparticular temperature-reducing scheme in step 185, the temperature ofthe coil controller 24 is monitored (step 187). Should the temperaturerise above a safe temperate (Tmax), which might indicate that the chosentemperature-reducing scheme in step 185 is insufficient, a differenttemperature-reducing scheme (e.g., another of the techniques from FIGS.4-9) can again be tried in step 189. In other words, a first algorithmfor charging both batteries is used first (185) followed by a secondalgorithm for charging both batteries (187) should the temperaturebecome too high.

Although disclosed in the context of a multi-electrode microstimulator,it should be understood that the disclosed battery charging techniquescan have applicability to many other sorts of implantable medical devicesystem applications, including, drug pumps, cochlear implants,pacemakers, etc.

It should be noted that the control circuitry, e.g., microcontroller 60(e.g., FIG. 3A) can comprise any number of logic circuits, whichcircuits can be discrete and coupled together, or which can beintegrated in a traditional discrete microcontroller circuit. Eitherway, “circuitry in the external charger” as used in the claims should beconstrued as covering circuitry embodied in a microcontroller or amicroprocessor, or any other arrangement of logical circuit(s), whetherintegrated or not, for performing the necessary control functionsrequired by the claims. Moreover, “circuitry in the external charger” asused in the claims can be the same or different from other circuitsrecited as being “circuitry in the external charger” depending oncontext and on the control functions as recited by the claims.

While the invention herein disclosed has been described by means ofspecific embodiments and applications thereof, numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the literal and equivalent scope of the invention setforth in the claims.

1. A method for charging an implant battery in an implantable medicaldevice and an external battery in an external charger, comprising: usingcircuitry in the external charger to determine that both the externalbattery in the external charging device and the implant battery in theimplantable medical device require charging; using circuitry in theexternal charger to enable charging a first battery comprising eitherthe external battery or the implant battery while disabling charging ofa second battery comprising the other of the external battery or theimplant battery; and upon determining using circuitry in the externalcharger that the first battery is charged to a pre-determined level,using circuitry in the external charger to disable charging of the firstbattery while enabling charging of the second battery.
 2. The method ofclaim 1, wherein charging the external battery is enabled or disabled byenabling or disabling a battery charging circuit in the externalcharger.
 3. The method of claim 1, wherein charging the implant batteryis enabled or disabled by enabling or disabling a wireless transmitterin the external charger which provides wireless power to the implantbattery.
 4. The method of claim 1, wherein the circuitry in the externalcharger comprises a microcontroller.
 5. The method of claim 1, whereinthe predetermined level comprises a voltage for the battery beingcharged.
 6. The method of claim 1, wherein determining that the implantbattery requires charging requires telemetry of an implant batteryvoltage from the implantable medical device to the external device.
 7. Amethod for charging an implant battery in an implantable medical deviceand an external battery in an external charger, comprising: usingcircuitry in the external charger to determine that both the externalbattery in the external charging device and the implant battery in theimplantable medical device require charging; and using circuitry in theexternal charger alternate between charging of the external battery andthe implant battery.
 8. The method of claim 7, wherein the externalbattery is charged for a first time period, and wherein the implantbattery is charged for a second time period.
 9. The method of claims 8,wherein the first and second time periods are equal.
 10. The method ofclaim 7, wherein both the external battery and implant battery arecharged using a DC voltage derived from an AC power source.
 11. Themethod of claim 7, further comprising upon determining using circuitryin the external charger that one of the external battery or the implantbattery is charged, using circuitry in the external charger to enablecharging of the other of the external battery of the implant batterywhile disabling charging of the charged battery.
 12. The method of claim7, wherein the implant battery is charged using a wireless transmitterin the external charger.
 13. A method for charging an implant battery inan implantable medical device and an external battery in an externalcharger, comprising: using circuitry in the external charger todetermine that both the external battery in the external charging deviceand the implant battery in the implantable medical device requirecharging; and using circuitry in the external charger to control theexternal charger to simultaneously charge the external battery and theimplant battery, wherein the external charger controls charging ofeither or both of the external battery and the implant battery at alower average power level than would be used were either battery to becharged by itself.
 14. The method of claim 13, wherein the externalbattery is charged at a lower average power level.
 15. The method ofclaim 14, wherein the external battery is charged at a lower averagepower level by reducing its average charging current.
 16. The method ofclaims 15, wherein the reduced average charging current comprises aconstant current less than a constant current that would be used tocharge the external battery without simultaneous charging of the implantbattery.
 17. The method of claim 15, wherein the reduced averagecharging current comprises a time varying current which on average islower than a current which that would be used to charge the externalbattery without simultaneous charting of the implant battery.
 18. Themethod of claim 13, wherein the internal battery is charged at a loweraverage power level.
 19. The method of claim 18, wherein the internalbattery is charged by activating a wireless transmitter within theexternal charger, and wherein the transmitter is powered at a loweraverage power level by using a power supply voltage less than a thepower supply voltage that would be used without simultaneous charging ofthe external battery.
 20. The method of claim 13, wherein the internalbattery is charged by activating a wireless transmitter within theexternal charger, and wherein the transmitter is powered at a loweraverage power level by duty cycling the transmitter.
 21. A method forcharging an implant battery in an implantable medical device and anexternal battery in an external charger, comprising: using circuitry inthe external charger to determine that both the external battery in theexternal charging device and the implant battery in the implantablemedical device require charging; and using circuitry in the externalcharger to simultaneously charge the external battery and the implantbattery at full power levels; using circuitry in the external charger toassess a temperature of the external charger; if the assessedtemperature exceeds a predetermined temperature, using circuitry in theexternal charger to charge one or both of the external battery or theimplant battery at less than their full power levels.
 22. The method ofclaim 21, wherein the full power levels comprises power levels at whichthe external battery or the implant battery would be individuallycharged were the other battery not being simultaenously charged.
 23. Themethod of claim 21, wherein lowering the power level comprises loweringthe power supply voltage of a transmitter in the external charger whichwirelessly provides power to the implant battery, or comprises loweringa power supply voltage used to charge the external battery.
 24. A methodfor charging an implant battery in an implantable medical device and anexternal battery in an external charger, comprising: using circuitry inthe external charger to determine that both the external battery in theexternal charging device and the implant battery in the implantablemedical device require charging; and activating a first algorithm in theexternal charger for charging the external battery and the implantbattery; using circuitry in the external charger to assess a temperatureof the external charger; if the assessed temperature exceeds apredetermined temperature, activating a second algorithm in the externalcharger for charging the external battery and the implant battery. 25.The method of claim 24, wherein the first algorithm comprises chargingthe external battery and implant battery simultaneously, but wherein thesecond algorithm does not charge the external battery and the implantbattery simultaneously.
 26. The method of claim 25, wherein the firstalgorithm charges the external battery and the implant battery at acombined first power levels, but wherein the second algorithm chargesthe external battery and the implant battery at a combined second powerlevel less than the first power level.
 27. The method of claim 24,further comprising using circuitry in the external charger to assess atemperature of the external charger after activation of the secondalgorithm; if the assessed temperature is below the predeterminedtemperature, activating the first algorithm.
 28. An external charger forinterfacing with an implantable medical device, comprising: a batterycharging circuit for controlling the charging of an external battery inthe external charger; a transmitter for controlling a wirelesstransmission to the implantable medical device, wherein the wirelesstransmission provides power to charge an implant battery in theimplantable medical device; control circuitry for implementing analgorithm to selectively enable the battery charging circuit and thetransmitter in the event that the control circuitry determines that boththe external battery and the implant battery requires charging.
 29. Theexternal charger of claim 28, wherein the algorithm first enables one ofthe battery charging circuitry or the transmitter to respectively fullycharge the external battery or the implant battery, and then fullycharges the other of the external battery of the implant battery. 30.The external charger of claim 28, wherein the algorithm alternatesbetween enabling the battery charging circuitry and the transmitter torespectively alternate between the charging of the external battery andthe implant battery.
 31. The external charger of claim 28, wherein thealgorithm enables both the battery charging circuit and the transmittersimultaneously, but reduces an amount of power to either or both of thebattery charging circuitry and the transmitter.
 32. The external chargerof claim 28, further comprising a temperature sensor for indicating atemperature to the control circuitry.
 33. The external charger of claim32, wherein the control circuitry implements a different algorithm toselectively enable the battery charging circuit and the transmitter inthe event that the control circuitry determines that a pre-determinedtemperature has been exceeded.
 34. The external charger of claim 28,further comprising a switch for passing either a voltage of the externalbattery or a DC voltage as generated from an AC power source to thetransmitter.
 35. An external charger for interfacing with an implantablemedical device, comprising: a battery for producing a battery voltage;an AC power source for producing a DC voltage, wherein the DC voltage isusable to charge the battery; and a transmitter for providing powerwirelessly to charge a battery in an implantable medical device, thetransmitter comprising a resonant circuit powered by a power supplyvoltage, wherein the power supply voltage is selectable between thebattery voltage and the DC voltage.
 36. The external charger of claim35, wherein the power supply voltage is selected as the DC voltage ifthe battery voltage is below a pre-determined level, but is selected asthe battery voltage if the battery voltage is above a pre-determinedlevel.